Author Topic: lm 324 upgrade  (Read 11211 times)

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Offline Kevin.D

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lm 324 upgrade
« on: March 24, 2013, 08:38:46 am »
Does any one know a good upgrade replacement for the lm 324 op amp. ?
Heres what im' looking for
It must be single supply capable upto at least 30V
 like LM324 common mode input MUST at least include GND ,And output must go to gnd .
Have a decent input offset voltage < 0.5 mV (lm324 is 2 mV)
 Have good  low input bias current spec . < 10nA max . (lm324 is 100nA)
High speed is not so important ,as long as it's no slower than lm324 .
Also it must be cheap and easily available .
Could do with it being available in dual and quad versions.

I am fed up with looking and not finding anything ,everything seems to be made for low voltage , these days .
Been looking at the LT1014 which supposed to be an precision lm324 but ,it's not that much of an upgrade really ,the input bias current is 50nA which is still to high .
 
 

Offline AndyC_772

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Re: lm 324 upgrade
« Reply #1 on: March 24, 2013, 09:21:14 am »
A few minutes on Linear Tech's parametric search yields this:.

Should get you started...
« Last Edit: March 24, 2013, 09:23:12 am by AndyC_772 »
 

Offline free_electron

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Re: lm 324 upgrade
« Reply #2 on: March 24, 2013, 11:33:43 am »
lmc66xx series ?
Professional Electron Wrangler.
Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline amspire

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Re: lm 324 upgrade
« Reply #3 on: March 24, 2013, 03:28:47 pm »
There is no direct replacement for a LM324 family, since no other opamp family can safely handle voltages on the inputs well over the positive supply. The LT1014 is not a direct replacement. If you are replacing the LM324 opamp in an existing design, you need to check the circuit to see if the inputs are always below the positive supply.

For new designs, you will be very much better off if you can redesign for a 5V supply. There are not a lot of options for 30V supply opamps, and I am not sure if any are cheap.

The opa118/2188/4188 families are very nice but I wouldn't call them cheap. Same with the LT opamps.
 

Offline konfu

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lm 324 upgrade
« Reply #4 on: March 24, 2013, 06:14:46 pm »
LT6016 & LT6017.

no direct replacements but great devices! might be a bit more costy but I haven't found ones with better specs for higher voltages yet. linear technology is quite easy to sample as well...
 

Offline bingo600

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Re: lm 324 upgrade
« Reply #5 on: March 25, 2013, 03:28:52 am »
Are they that bad  :palm:

I bought 1000 (SGS) in SO14 , for 55$ a few years ago on 'Bay...

We ought to do a component exchange section  8)

/Bingo
« Last Edit: March 25, 2013, 05:33:25 am by bingo600 »
 

Offline Zlatko

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Re: lm 324 upgrade
« Reply #6 on: March 25, 2013, 09:57:38 am »
LT1491 Direct replecment much better performance
 

Offline amspire

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Re: lm 324 upgrade
« Reply #7 on: March 25, 2013, 02:47:39 pm »
LT1491 Direct replecment much better performance
Wow! Well done for spotting this chip.

The inputs have an even better overvoltage then the LM324. Up to 44V positive (regardless of supply voltage) at a very low bias current and it can safely handle -22V below the negative rail through an internal 1K resistor to diodes to 0V rail.

That is brilliant! It has two parallel input stages - NPN and PNP which I think give it ac active common mode range of probably 0.3V below the negative rail to 0.3V above the positive supply rail.

Much slower then the LM324 so it is only a replacement for very slow LM324 circuits, but I will definitely keep this opamp on my short list.

Richard
 

Offline codeboy2k

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Re: lm 324 upgrade
« Reply #8 on: March 25, 2013, 05:03:57 pm »
I'll keep the LT1491 on my radar as well for when it's needed.  It's quite pricey at $3.26 each for a reel of 2500 from Digikey so I'd have to be damn sure I needed it.  You just can't beat the LM324 for it's price... $0.10 each for a reel of 2500, and when it fits the circuit and you can live with it's specs and/or calibrate them out, then it's a clear winner to choose the LM324, even for new designs (although many datasheets say not recommended for new designs, they are still producing them )



 

Offline amspire

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Re: lm 324 upgrade
« Reply #9 on: March 26, 2013, 12:36:20 pm »
Is their some particular reason why having inputs that can extend beyond the rails is so desirable? You are still exceeding the CM input range so the output will not be the representation of the input you intended, it will just clip.
Yes. If the inputs exceed the specified maximums, the opamp IC can latch that usually means it self destructs. So if your opamp circuit does connect to an externally power circuit that under some circumstances (eg power up) can drag an input more then 0.3V above the positive rail or 0.3V below the negative rail, then you do have to add a series resistor and a pair of external schottky diodes. You cannot rely on the inherent IC diode junctions as it it those junctions that cause the latchup in the first place.

What this means is that if you use conventional opamps in a circuit with multiple supply rails, and assume the supplies power up at different rates, you have to make sure that on power up, an opamp input can never go above or below the supply rails. With a LM324, you do not have to worry about this for positive overvoltages. With the LT1491, a 1K series resistor with the input means it is safe for positive and negative overvoltages.

As another example, I used LM324s in my power supply project. This means that I can have a 12V battery on the output, and switch off the power supply, and the LM324's can cope with the 12V from the battery fine without loading the battery. With almost all other opamps, I would have to add a series resistor, and the schottky diodes, and they would load the battery. In many supply designs, they get around this problem by using a reverse-biased diode that goes from the load output back to the supplies power rail which means that if the supply is off, and you attach a 12V battery, the battery is actually powering the power supply.

It is a nice feature. If you do not have overvoltage, you just have to make different design choices. That is all.

In the context of this thread, if you want to replace a LM324 in an existing design, you have to keep in mind that the designer of the original design may be using the LM324's overvoltage capability. If the design does not use this property, then replacement is probably not hard.

Richard.
 

Offline codeboy2k

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Re: lm 324 upgrade
« Reply #10 on: March 27, 2013, 06:01:56 am »
You don’t even have to buy 2500 of them for sub 10 cent pricing.

LM324DR

Oh wow it's on sale at .097 for QTY 1  :-+ 

Since I don't have a project at the moment where I need 2500, I'll have to add a few to my parts bin at this price :)
 

Offline Kevin.D

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Re: lm 324 upgrade
« Reply #11 on: March 28, 2013, 12:23:07 am »
LT1491 Direct replecment much better performance
Well it's got some good specs , low power aswell , it's slow though , slower than LM324 .
The LT1639 looks to be the higher speed version of this device ,roughly same speed as the lm324 ,but it also has a higher input bias current which lets it down,only 50% better than the LM324 ,it's seems to be a direct replacement I think. As long as the extra rail to rail capability  is not going to cause a problem .

Thanks for the replies guys
 

Offline amspire

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Re: lm 324 upgrade
« Reply #12 on: March 28, 2013, 01:06:27 am »
If I understand the specs correctly, the LT1491 and the LT1639 will not only withstand overvoltage on the inputs, but they keep operating with overvoltage on the inputs.

So they can still operate with both inputs at 44V with the opamp running from a +5V supply.

The input bias current increases from 20nA to to 8uA (as the input NPN transistors saturate and so they are now just forward biased diodes into the emitters of the next PNP stage) and the offset voltage increases to 2mV, but the inputs are still fully functioning in differential mode.

That is pretty amazing. I am more impressed now.

One thing you have to watch is the changes in bias current. In a normal opamp, the bias current is always in one direction and is fairly constant. In these opamps, the bias current goes from -20nA for 0.8V below the +Vs rail  to +40uA between +Vs - 0.5V to +Vs and then 8uA up to +44V.

If you were using a 1M input resistor, this would correspond to voltage drops across the 1M input resistor of  -0.02V, +0.04V and 8V (ouch!).

Richard.
 

Offline Zlatko

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Re: lm 324 upgrade
« Reply #13 on: March 30, 2013, 05:01:21 am »
I use LT1490 dual opamp at the moment in Dave Supply schematic rev.C because i cannot manage to make it work with LM358 (N and P versions). And works perfectly. If u need 1 or 2 for testing purposes u can order from Linear as free sample.
 

Offline dotneck335

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Re: lm 324 upgrade
« Reply #14 on: November 26, 2015, 04:26:45 pm »
The LMC660 is pin-for-pin compatible with the LM324 and offers greater bandwidth and input resistance over the LM324. These features
will improve the performance of many existing single-supply applications. Note, however, that the supply voltage
range of the LMC660 is smaller than that of the LM324.
 

Offline Aeternam

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Re: lm 324 upgrade
« Reply #15 on: April 26, 2016, 01:39:15 am »
I'm digging out this thread because I need a noobie reality check on opamp datasheet grammar.

Am I correct in assuming that I'm looking for

Voh (output swing high) = V+ and
Vol (output swing low) = GND

when hunting for a rail-to-rail single-supply opamp? Further, that these values change (unfavorably) with load?
 

Offline macboy

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Re: lm 324 upgrade
« Reply #16 on: April 27, 2016, 03:47:51 am »
There is no direct replacement for a LM324 family, since no other opamp family can safely handle voltages on the inputs well over the positive supply. ...
Plenty do this. Search for "Over the top" or OTT inputs.
 


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